That depends on how you plan to use them.
up til now, 60 pts of skinks were used to:
- fill battleline
- occupy objectives with their speed
- serve as screen unit
- no combat at all, can annoy opponent with the wary fighter ability
but now, skinks are 70 and knights are 80, so it's a matter to see if 5 knights can cover the same role as 10 skinks:
- fill battleline: check
- occupy objectives with their speed: check… and they can move up to 14", so they're even better
- serve as screen unit: check… and they do it better than skinks, as they cover more or less the same room, but got a better save.
- no combat at all, can annoy opponent with the wary fighter ability: no wary fighter, but knights can actually fight, so they can effectively defend an objective, while skinks were forced to flee even if faced by 10 skeletons.
So yeah. 60 pts vs 90 pts: 10 skinks were better… but 70 vs 80 pts? I'll pick the knights.
and knights got more support by synergies than skinks (see serpent's staff, battalions and so on)